Vehicle manufacture may be conducted in a variety of ways. In for example the car industry the manufacturer usually produces vehicles which are complete and intended for direct delivery to final customers.
The heavy vehicle industry, however, commonly also employs other kinds of production methods. Manufacturers of heavy vehicles may, as in the car industry, produce vehicles intended for delivery directly to final customers or the vehicle's final user, but it is also very common that vehicles produced by the manufacturer are only completed to a certain extent, with a view to being subsequently completed by a customer of the manufacturer, e.g. a third party supplier, in such a way as to meet specific requirements. It may also be that the vehicle, although substantially completed by its manufacturer, will be provided with further functionalities, e.g. by another party such as a third party supplier or final user, before it is put into use.
It is for example usual that commercial vehicle manufacturers, as well as producing fully equipped vehicles, produce also versions comprising only the chassis, or chassis and cab, with a view to subsequent completion by another party according to the latter's specific requirements.
For example, chassis produced by a vehicle manufacturer may be such as to be usable in any desired way as bases for building on in order to construct mobile homes, fire vehicles, ambulances, concrete mixer trucks, refrigerated vehicles etc.
Moreover, a bus chassis for example may be produced by the vehicle manufacturer with little or no bodywork, with a view to subsequent building on by a bus bodybuilder.
Thus the building-on carried out by another party may be very extensive and at least some building-on is also very common in the case of heavy vehicles. For this reason, the vehicle manufacturer often also to a great extent prepares the vehicle in such a way as to facilitate subsequent building-on. For example, one or more power takeoffs (PTOs) are often provided, e.g. so that built-on elements can be connected to the vehicle's engine and/or gearbox to enable them to be provided with driving power from the vehicle. There may also be connections to make it possible to use, for example, the vehicle's electrical system, hydraulic system and/or pneumatic system for implementation of built-on functions.
A vehicle may thus be provided with a plurality of PTOs, and the power offtake requirement may vary depending on the kinds of applications built onto the vehicle. Certain applications may for example require power which is constantly available when the vehicle's engine is running, irrespective of whether the vehicle is moving or not, e.g. in the case of concrete mixer trucks, refrigeration units in refrigerated vehicles and plough systems. Other applications will only need power on distinct occasions, e.g. upon activation of a crane etc.
The activation of a PTO for, and hence the operation of, one or more built-on functions is often not such that continuous or unregulated power offtake is desirable, since it is only usually required in certain situations, upon demand from the built-on element itself or from, for example, the vehicle's driver.
As well as PTOs as such, it is therefore usual for the vehicle manufacturer to provide a building-on interface to enable communication between the vehicle's internal communication systems and the built-on element's control system. This interface may for example comprise one or more terminal blocks with a number of inputs/outputs such that high/low signals on an output may for example represent the status of a certain function, and this information may be used as a control signal for conditional control of built-on functions. There may also be inputs, e.g. for conveying from the built-on element's control system a demand for activation of a certain PTO, in which case a high level may for example indicate a demand for activation and a certain input may have a defined meaning.
As a given chassis configuration may be used for built-on elements within a large number of areas of application, it is often not possible at the vehicle manufacturing stage to know the specific intended use of a specific chassis, still less the characteristics of specific build-on elements, e.g. a specific crane unit or a specific plough system.
Thus built-on functions may communicate their status, e.g. whether the function is active or inactive, by applying a voltage to an input on the interface to the vehicle's internal control system. The vehicle's internal communication system will thus also be aware that built-on functions exist and their status by the built-on function signalling a demand for activation of some vehicle function and/or demanding power.